This invention relates to an apparatus for measuring fuel injection advance angle in a diesel engine.
The measurement of fuel injection advance angle is necessary to effect closed-loop control of the fuel injection timing of a diesel engine. In general, a conventional apparatus for measuring fuel injection advance angle (injection timing) includes such an apparatus as shown for example in Japanese patent application Publication No. 53-65528 (which corresponds to U.S. Pat. No. 4,265,200, DE No. 2 653 046 and UKP No. 1 594 827, in which injection advance angle is measured based on the difference between the lift timing of a needle valve of a fuel injection valve and the top dead center timing of the piston of the engine. In this conventional apparatus, a needle valve lift sensor is mounted on the fuel injection valve of one of plural cylinders and a top dead center sensor is mounted on the crankshaft of the engine for outputting top dead center pulses in response to the top dead center timing of each of the pistons, and the injection advance angle is measured on the basis of the difference in timing between the lift timing pulse from the needle valve lift sensor and the corresponding top dead center pulse from the top dead center sensor. The needle valve lift sensor may, for example, be of the induction coil type which includes a voltage on a coil by the up-and-down motion of the needle valve or of the piezoelectric type which develops a voltage when pressure is applied on the piezoelectric element through the up-and-down motion of the needle valve. However, these types of sensors involve a problem in that the voltages obtained thereby are liable to have pulsive noise superposed thereon because of their high impedance and an error may be introduced into the measurement by the noise components.
The conventional apparatus has still another problem. The needle valve lift sensor picks up, with a time delay, vibrations caused by fuel injection in other cylinders having no needle valve lift sensor or picks up post-injection vibrations or other vibrations of the engine, and the picked up vibrations are output as a lift timing pulse(s), which may introduce an error into the measurement result of the injection advance angle when the level of the pulse is large.